The present invention relates to methods for propping complex fracture networks in tight subterranean formations.
After a wellbore is drilled, it may often be necessary to fracture the subterranean formation to enhance hydrocarbon production, especially in tight formations like shales and tight-gas sands. Access to the subterranean formation can be achieved by first creating an access conduit, such as a perforation, from the wellbore to the subterranean formation. Then, a fracturing fluid, often called a pad fluid, is introduced at pressures exceeding those required to maintain matrix flow in the formation permeability to create or enhance at least one fracture that propagates from at least one access conduit. The pad fluid is followed by a treatment fluid comprising a propping agent to prop the fracture open after pressure from the fluid is reduced. In some formations like shales, fractures can further branch into small fractures extending from a primary fracture giving depth and breadth to the fracture network created in the subterranean formation. As used herein, a “fracture network” refers to the access conduits, fractures, microfractures, and/or branches, man-made or otherwise, within a subterranean formation that are in fluid communication with the wellbore. As used herein, an “access conduit” refers to a passageway that provides fluid communication between the wellbore and the subterranean formation, which may include, but not be limited to, sliding sleeves, open holes in non-cased areas, hydrajetted holes, holes in the casing, perforations, and the like. The propping agents hold open the fracture network thereby maintaining the ability for fluid to flow through the fracture network to ultimately be produced at the surface.
In tight formations, especially those with high closure stresses, the size of the microfractures is often smaller than traditional propping agents. Therefore, once the fluid pressure is released the propping agent primarily maintains the fractures and branches of the fracture network while many of the microfractures close. In tight formations where microfractures are prevalent, this closure can significantly reduce the potential hydrocarbon material that can be produced from the subterranean formation before another fracturing and propping operation needs to be performed again, which can be expensive and time consuming.